Ethyl tertiary butyl ether has long been recognized as a suitable blending cosolvent for hydrous ethanol in gasoline stocks. See U.S. Pat. No. 4,207,076, for example, where ETBE has been blended into a fuel gasoline at about a 10 to 20 volume percent level, usually nearer 9 to 10%, in which the fuel comprises about 70 to 84% gasoline and 5 to 20% of 95% ethanol, i.e. grain alcohol. ETBE solubilizes grain alcohol in gasoline in all proportions thereby allowing a wide latitude in the precise amount of ethanol which can be blended with gasoline.
There has been considerable interest in the use of ethyl tertiary butyl ether (ETBE) as a lead free octane booster for gasoline. Note, for example, the following publications: Iburra et al., "Getting the Lead Out With Ethyl t-Butyl Ether," CHEM TECH, Feb. 1988, pp. 120-122 and Verbanic, "ETBE: Ethanol's Motor Fuel Hope?" CHEMICAL BUSINESS, Oct. 1988, at pp. 38-39 and the paper presented at the DeWitt Petrochemical Review, Houston, Texas, March 28-30, 1989, by Neerlich et al., entitled "Huels/UOP Technology for ETBE/MTBE Production." Recently, there has been increased interest in ETBE due to efforts in Washington D.C. to extend tax credits for corn-based ethanol used to produce ETBE.
It is known in the art to produce ETBE or MTBE by reacting isobutylene with either ethanol or methanol, resulting in the formation of ETBE or MTBE, respectively. The reaction normally is conducted in liquid phase with relatively mild conditions. The isobutylene can be obtained from various sources, such as naphtha cracking, catalytic cracking, etc. The resulting reaction product stream contains the desired MTBE or ETBE, as well as unreacted isobutene and other C.sub.4 hydrocarbons and methanol or ethanol.
A number of U.S. patents and allowed U.S. applications assigned to Texaco Chemical Inc. disclose methods of making alkyl tertiary alkyl ethers, including ETBE, in one step.
In U.S. Pat. No. 4,822,921, there is described a method for preparing alkyl tertiary alkyl ethers, including ETBE, which comprises reacting a C.sub.1 -C.sub.6 primary alcohol with a C.sub.1-C.sub.10 tertiary alcohol over a catalyst comprising an inert support impregnated with phosphoric acid.
U.S. Pat. No. 4,827,048 describes a method for preparing alkyl tertiary alkyl ethers from the same reactants using a heteropoly acid on an inert support.
U.S. Pat. No. 5,099,072 discloses a method for preparing alkyl tertiary alkyl ethers, including ETBE, over an acidic montmorillonite clay catalyst which possesses very specific physical parameters.
U.S. Pat. No. 5,081,318 discloses a method for preparing alkyl tertiary alkyl ethers by reacting a C.sub.1 -C.sub.6 primary alcohol with a C.sub.4 -C.sub.10 tertiary alcohol over a catalyst comprising a fluorosulfonic acid-modified zeolite.
U.S. Pat. No. 5,059,725 discloses a method for preparing alkyl tertiary alkyl ether, including ethyl tertiary butyl ether, from C.sub.1 -C.sub.6 primary alcohols and C.sub.4 -C.sub.10 tertiary alcohols over a catalyst comprising ammonium sulfate or sulfuric acid on a Group IV oxide.
U. S. Pat. No. 5,157,162 discloses a fluorosulfonic acid-modified clay catalyst for the production of ETBE, inter alia, from C.sub.1 -C.sub.6 primary alcohols and C.sub.4 -C.sub.10 tertiary alcohols.
In U.S. Pat. No. 5, 162,592 there is described a method for producing alkyl tertiary alkyl ethers from C.sub.1 -C.sub.6 primary alcohols and C.sub.4 -C.sub.10 tertiary alcohols using a multimetal-modified catalyst.
A hydrogen fluoride-modified montmorillonite clay catalyst is employed in U.S. Pat. No. 5,157,161 to produce alkyl tertiary alkyl ethers, including ETBE.
In U.S. Pat. No. 5,183,947 fluorophosphoric acid-modified clays are employed as catalysts in a method to produce alkyl tertiary alkyl ethers.
In U.S. Pat. No. 5,214,217 there is disclosed the use of a super acid alumina or a faujasite-type zeolite to produce alkyl tertiary alkyl ethers.
U.S. Pat. No. 5,214,218 discloses the use of a haloacid-modified montmorillonite clay catalyst to convert C.sub.1 -C.sub.6 primary alcohols and C.sub.4 -C.sub.10 tertiary alcohols to alkyl tertiary alkyl ethers.
Fluorophosphoric acid-modified zeolites are employed in U.S. Pat. No. 5,220,078 to produce alkyl tertiary alkyl ethers.
U.S. Pat. No. 5,243,091 discloses a method for continuous manufacture of MTBE from tertiary butyl alcohol and methanol using a peroxide contaminated feed wherein the peroxide contaminants are decomposed, then charged to a methyl tertiary butyl ether etherification reaction zone with methanol to form an isobutylene-containing MTBE etherification product that is substantially free from peroxide contaminants, wherein the byproduct isobutylene is utilized downstream of the etherification reaction zone as an extractant in the purification of MTBE and wherein by-product isobutylene is used as a reactant in the preparation of additional MTBE.
Other references in the art which disclose ETBE as a product usually require two stages rather than one and use isobutylene as a reactant.
U.S. Pat. Nos. which discuss the production of ETBE as well as MTBE include:
5,070,016 PA1 4,440,063 PA1 4,962,239 PA1 4,015,783
These patents all use isobutylene as the coreactant rather than t-butanol.
In U.S. Pat. No. 4,334,890, a mixed C.sub.4 stream containing isobutylene is reacted with aqueous ethanol to form a mixture of ethyl tertiary butyl ether (ETBE) and tertiary butyl alcohol (tBA).
U. S. Pat. No. 5,015,783 describes a process for producing ethers, including ETBE, which comprises passing a feed stream to an etherification zone, passing the etherification zone effluent stream to a distillation column and further involves cooling the overhead stream, refluxing and recycling.
In U. S. Pat. No. 5,248,836 there is disclosed a process for selective etherification of isobutylene with EtOH to form ETBE in a distillation column reactor containing a fixed bed acid cation exchange resin as a catalytic distillation structure in a reaction distillation zone combined with a straight pass fixed bed reactor.
A process for the production of ETBE and/or MTBE is disclosed in U.S. Pat. No. 2,480,940.
U.S. Pat. No. 5,292,964 discloses a process for production of methyl tertiary butyl ether or ethyl tertiary butyl ether which comprises reacting tertiary butyl alcohol with a lower alcohol selected from methanol or ethanol in an etherification zone and forming an etherification effluent containing lower alkyl tertiary butyl ether, water of reaction and lower alcohol, passing the etherification effluent to a distillation zone and distilling the effluent from the first step to separate an overhead mixture of ether and lower alcohol substantially free of water from a bottoms comprised of tertiary butyl alcohol, lower alcohol and water; and reacting a lower alcohol/ether admixture from said overhead mixture with isobutylene in a second etherification zone to form lower alkyl tertiary butyl ether.
Macroreticular Acid Resins
Acid resin catalysts are known in the art. They are discussed, for example in U.S. Pat. Nos. 4,629,710 and 3,862,258, incorporated herein by reference.
Acidic cation exchange resins are used in U.S. Pat. No. 4,504,687 in a method for producing tertiary ethers from C.sub.4 or C.sub.5 streams containing isobutene and isoamylene respectively in a process wherein the acidic cation exchange resin is used as the catalyst and as a distillation structure in a distillation reactor column, wherein the improvement is the operation of the catalytic distillation in two zones at different pressures.
Pentasil Zeolites
The characteristic structures of catalytically important molecular sieve zeolites are discussed in "Molecular Sieve Catalysts," by J. Ward, Applied Industrial Catalysis, Vol. 3, Ch. 9, p. 271 (1984). Molecular sieve zeolites which have been investigated in most detail are those which have achieved industrial application, namely, X, Y, mordenite, the pentasil types and erionite.
The pentasil family of zeolites contains a continuing series of which ZSM-5 and ZSM-11 are end members. See T. E. Whyte et al. "Zeolite Advances in the Chemical and Fuel Industries: A Technical Perspective," CATAL. REV.-SCI. ENG., 24,(4), 567-598 (1982).
The article by J. W. Ward, supra, presents an excellent review of pentasil type zeolites. The pentasils usually have a Si/Al ratio greater than 10. A more detailed description of pentasil zeolites follows under the "Description of the Catalyst."
A good overview of applications for zeolites, including pentasil type zeolites is found in an article titled, "Zeolite Catalysts Face Strong Industrial Future", European Chemical News, 10 Jul. 1989, p. 23. For example, medium pore H-ZSM-5 is sometimes added to a zeolite Y catalytic cracking catalyst to increase the aromatics content and hence motor octane, of the gasoline fraction. In the limited space of ZSM-5, where two pore systems of about 5-6 .ANG. in diameter intersect to give spatial regions of around 9 .ANG. diameter at the intersections, there is a cutoff around C.sub.10 to C.sub.11 for products from transformation of a wide range of feedstocks, including alkanes, olefins and alcohols.
ZSM-5 is a catalyst used for converting methanol to gasoline, processing C-8 streams, selectively isomerizing m-cresol to p-cresol, suppressing the formation of diphenylalanine in the production of aniline, and producing pyridine and .beta.-picoline from acetaldehyde, formaldehyde and ammonia.
In an Article titled "Shape Selective Reactions with Zeolite Catalysts", J. CATAL., 76, 418 (1982), L. B. Young et al. report data on selectivity in xylene isomerization, toluene-methanol alkylation, and toluene disproportionation over ZSM-5 zeolite catalysts. Some of the ZSM-5 zeolites in this study were modified. It was demonstrated that appropriately modified ZSM-5 class zeolites are capable of generating uniquely selective compositions. Intrinsic reactivities and selectivities are considerably altered with these modified catalysts.
There is a discussion of the shape selective properties of ZSM-5 in "A Novel Effect of Shape Selectivity: Molecular Traffic Control In Zeolite ZSM-5", by E. G. Derouane, et al., J. CATAL., 65, 486 (1980) Some of the observations included the following: (i) linear aliphatics diffuse rather freely in the ZSM-5 framework and can be adsorbed in both channel systems; (ii) isoaliphatic compounds experience stearic hinderance which may restrict their diffusion in the sinusoidal channel system; and (iii) aromatic compounds and methyl substituted aliphatics have a strong preference for diffusion and/or adsorption in the linear and elliptical channels.
E. G. Derouane et al. studied shape selective effects in the conversion of methanol to higher hydrocarbons and alkylation of p-xylene on pentasil-family zeolites. Some of these zeolites were modified by the incorporation of phosphorous, or embedded in a silica filler. Their findings are reported in "Molecular Shape Selectivity of ZSM-5, Modified ZSM-5 and ZSM-11 Type Zeolites", in FARADAY DISCUSSIONS 72, 331 (1981)
It has been reported in the art that methyl t-butyl ether could be prepared from isobutylene over zeolite catalysts.
P. Chu et al. report results of one study in "Preparation of Methyl tert-Butyl Ether (MTBE) over Zeolite Catalysts", IND. ENG. CHEM. RES., 26, 365 (1987). They reported that ZSM-5 and ZSM-11 have been identified to be highly selective zeolite catalysts for the preparation of MTBE from isobutylene. Compared to the conventional commercial catalyst, AMBERLYST.RTM. 15 resin, the pentasil zeolites are thermally stable, give no acid effluent and are less sensitive to the methanol-to-isobutene ratio. The excellent selectivity is believed to be effected by the size of their pore structure, which provides easy access to methanol and restricted access to isobutene. In contrast, small pore zeolites such as synthetic ferrierite were found inactive. Large pore zeolites, such as high-silica mordenite and zeolite Beta were not expected to exhibit shape selectivity.
Another reference which discusses the use of pentasil zeolites in MTBE service is by G. H. Hutchings, et al., CATAL. TODAY, 15, 23 (1992).
There remains in the art a need for a method of producing ethyl tertiary butyl ether from ethanol and tert-butanol in one-step which avoids dehydration of isobutylene in a separate process. It would constitute a great advance in the art if it were possible to accomplish the conversion in one step while, at the same time obtaining 40-70% yield of ETBE and high selectivity from ethanol continuously. It would also be advantageous if such a process and the advantages mentioned could be accomplished at a low temperature.